On 11 subjects, members of an Himalayan expedition, observations have been collected on maximum oxygen consumption (\(\dot V_{O_2 } ^{\max } \)) and some respiratory and circulatory characters at sea level and at altitude after a 60 days acclimatization period. The most striking changes as compared with the sea level values (= 1.00) are: a) a fall in the maximum exercise ventilation to ab. 0.78; b) a fall in the energetic efficiency of respiration to ab. 0.55; c) a fall of the vital capacity to ab. 0.87; d) a fall of the PACO2 to 0.55; e) an increase of blood haemoglobin to 1.32; f) a decrease of the VO2max to ab. 0.44 and g) a decrease of the maximum heart rate to ab. 0.80.